1. Technical Field
The present invention relates generally to magneto resistive elements and in particular to stripe height calibration of magneto resistive elements. Still more particularly, the present invention relates to a method and system for performing accurate, result-directed/predictive stripe height versus resistance calibration of magneto resistive sensors during lapping operation.
2. Description of the Related Art
Many direct access storage device manufacturers employ thin film magnetic recording heads. Conventional thin film read/write heads in data storage systems generally include an inductive write head in combination with either an inductive or magneto resistive (MR) read head. One type of MR/inductive head includes an inductive write head formed adjacent to a MR read head. In manufacturing such heads, rows of magnetic recording transducers are deposited simultaneously on wafer substrates using semiconductor type process methods. Subsequent to these depositions, the wafers are fabricated into rows of single element heads called slider rows. When separated from the slider rows, each slider contains magnetic read/write components and an air-bearing surface configured to aerodynamically xe2x80x9cflyxe2x80x9d over the surface of a spinning magnetic disk medium. The rows are separated by kerfs that facilitate subsequent slicing into individual sliders.
Commonly assigned U.S. Pat. No. 5,531,017 describes the process by which a wafer consisting of multiple slider rows is divided into quads of 29 slider rows prior to completing the lapping process. A number of such rows of sliders are deposited together onto a single semiconductor-type wafer, which is then cut into pieces commonly termed xe2x80x9cwafer quadrantsxe2x80x9d (or just xe2x80x9cquadrantsxe2x80x9d). A wafer quadrant is then bonded onto an extender tool (also sometimes known as a row tool, transfer tool, or support bar) and the foremost slider row is lapped as a unit on an abrasive surface, such as a plate coated with an appropriate slurry mix. The slider row is then cut from the wafer quadrant, so that lapping of a new foremost slider row may commence. The sliced off row of sliders is ready for additional manufacturing steps, dicing into individual sliders, and then the final steps which ultimately produce working disk drive heads.
As a further enhancement to this process, commonly assigned U.S. Pat. No. 6,174,218 describes the manner in which the quads are placed on an extender tool that is bendable so that the slider rows may be straightened out while the lapping operation is being completed. This process of bending the quad while lapping is also referred to as a bow compensated lapping (BCL) process. Extender tools provide a mechanism for holding the row of sliders while lapping or grinding operations are performed to produce an air bearing surface. Typically the slider rows distort from a co-linear line according to the internal stress of the wafer material and the surface stresses developed when reducing the wafers to slider rows. Further distortion of the rows of sliders from a co-linear line can occur as a result of the tool bonding operation. The combined stress distortion and bonding distortion of slider rows results in a total distortion or curvature condition called row bow.
Row bow may cause a row of sliders to be non-uniformly lapped during the lapping process. As such, this row bow condition can detrimentally affect critical head performance parameters, such as stripe height in MR heads, and throat height in inductive heads. To achieve optimum performance of MR/inductive heads, both the stripe height and throat height must be tightly controlled.
In order to control the amount of lapping performed on a slider row and to accurately determine the final MR element height (at the conclusion of lapping), the resistance must be known. Thus, the lapping process is controlled by the measured resistance of the MR elements in a slider row. The measured resistances are used for controlling the degree of lapping for each of the MR elements in a slider row to compensate for row bow. The electrical resistance is related to the desired MR element height (also referred to as stripe height), and the lapping process is terminated when the desired MR element height is reached.
FIGS. 1 and 2 illustrate two current configurations of lapping control systems, which both utilize resistance measurements to control the lapping process. In FIG. 1, a dual element, wire bonded electrical lapping guide (ELG) 103 (with both long or short elements) is placed in each kerf between MR elements 101 in a slider row. The MR elements are wire bonded to electrical contacts so that the resistance can be measured. This configuration is primarily utilized with wafers having a density of 36 slider rows and relatively large kerfs.
With the introduction of higher density wafer designs (e.g., the 44 slider row per wafer designed by International Business Machines), the increased row density resulted in narrower kerfs and restricted the placement of the dual element ELG studs in the kerfs. The dual element ELGs were therefore replaced with alternating long and short ELGs placed in adjacent kerfs. Thus, as shown in FIG. 2, the long ELGs 204 and short ELGs 203 were placed within the kerfs of MR elements 201 and utilized in the calibration process.
Further development in calibration systems led to the introduction of row level kiss lap (or flatness control lapping), which made it necessary to utilize element predicted stripe height for process control. However, at this juncture, it was discovered that due to lead current crowding and other physical characteristics in current MR devices, simple linear calibration methods no longer produced valid and/or accurate results.
In response, a higher order method of calibration called (abc) (i.e., calibration in which the constants of a quadratic equation are first determined) was introduced, which utilizes wafer resistance data (from MR elements) and resistance and stripe height data after a first BCL operation. One problem with this technique is that it is greatly compromised by the lack of MR resistance sensitivity to stripe height at the wafer level.
Another problem is that the technique mixes data from unlike structures. Thus, wafer element data utilized has unlapped and undisturbed edges as illustrated in FIG. 3B, while the same element measured after lapping (shown in FIG. 3C) has a lower stripe edge that provides completely different data from the wafer data structures of FIG. 3B. This difference is depicted by the graph on FIG. 3A. Thus, a non-linearity exists, which affects the results of the lapping operation.
Still another problem with using post-BCL data to calibrate MR elements is that post-BCL calibration can only be determined after first lapping the rows. Since, for accurate results, it is preferred to complete lapping based on measure resistance and stripe height (i.e., result-directed/predictive lapping), element calibration after BCL is too late.
Because of the above stated issues/problems with current (abc) lapping processes, the (abc) method does not provide adequate methods for result-directed/predictive lapping and is not an adequate calibration method for carrier stripe height control to the 0.05 micron 3 sigma regime required for the newer products being produced in 2002 and beyond.
The present invention thus realizes that it would be desirable to provide a method and lapping control system/process that provides more accurate responses to and/or representation of the relationship between resistance and stripe height of magneto resistive elements being lapped. A method and lapping control system that enables in-situ (predictive) calibration of the lapping operation on MR elements utilizing accurate, predicted relationship data between stripe height and resistance would be a welcomed improvement. It would be further desirable to provide a calibration system design that enables collection of more accurate resistance data without wire bonding for utilization in result-directed/predictive calibration. These and other benefits are provided by the invention described herein.
Disclosed is an in-situ (result-directed/predictive) magneto resistive (MR) stripe height calibration method capable of operating on-the-fly during lapping operation. The method involves utilization of an interval sampling technique, which provides a high number of data points on each row of thin film magneto resistive devices. The high number of data points are collected by interpolating data during a lapping operation using element-like ELGs (ELEs). The high number of data points generated are filtered and averaged at each key location to provide a much higher calibration accuracy than previously available. The primary advantage is to create an accurate relationship between MR element resistance and its stripe height while the MR element is being lapped. The method thus provides the ability to target either resistance or stripe height or a combination of both during the lapping process. Finally, the calibration system is completely self-contained and does not require wafer data.
Key to the invention is the design and utilization of element like ELGs (ELEs) which are strategically placed in alternating kerfs to provide significantly more accurate resistance data sensors. Thus, approximately half of the kerfs are populated with ELEs. The lapped head of the ELEs are made similar to the MR sensors. Use of the ELEs eliminates the need for wire bonding of the ELGs to the MR sensors as was done in the prior art. In the illustrative embodiments, the ELEs are placed in between a long and short ELG. The ELGs are utilized to calibrate stripe height and the ELEs are utilized (along with the MR sensors) to measure resistance corresponding to ELG stripe height. The collected data is analyzed by the controller/processor, which generates the constants that are used for determining stripe height by ELE or element resistance. These constants may define a linear, exponential, polynomial, power, or other relationship between stripe height and resistance.
In preferred embodiments, ELEs stripe heights are located lower than the MR elements. This allows for ELE resistance data collected at stripe heights that are equal to or lower than nominal stripe heights at the second lapping operation (kiss lap). If positioned equal to final kiss lap operation, first lapping operation can be terminated by desired final kiss lap resistance by ELEs when in resist lapping mode. If positioned lower than final kiss lap operation, for example at lower stripe height limit, ELE resistance will pass through nominal resistance, to preview final resistance before termination of first lapping operation. Ultimately ELEs located lower than MR devices provide a means for superior (abc) calibration because resistance data collected, covers more of, or all of the final stripe height distributions. It is by this means that proposed (abc) calibration better accounts of non-linearity between ELGs and ELEs.
The stripe height data is collected utilizing a plurality of electrical lapping guides (ELGs) and the resistive data values are simultaneously collected utilizing the ELEs. The ELEs are positioned in alternating kerfs with the ELGs and in the preferred embodiment, are positioned with their sensors at a predetermined height below the level of the MR element. The invention thus enables the lapping operation to preview MR element resistance and stripe height at their final post kiss lap target. The ELEs read values of resistance to derive the calibration constants. The constants are fed forward to the next lapping operation to determine the stripe height using the MR resistance values. The higher density ELE collection leads to predictive capability. According to one embodiment, the ELEs are positioned at a lower vertical level than the MR elements. The ELE MR back edge distance below the MR element back edge is equal to the MR material removal of the next lapping operation. This permits the calibration system to be utilized to predict the resistance results prior to the final kiss lapping, and thus enables a better predictive lapping operation.
The calibration algorithm thus performs an interpolation between the ELEs (and not an extrapolation as would be required when the ELEs are placed at the row level). Once the accurate relationship is calculated, however, calibration/adjustment of the lapping components (e.g., actuators) is passed to the ELEs. Each lapping operation laps to the ELEs and accurate data is collected. A more accurate prediction of resistance versus stripe height relationship is thus provided.
As recited within the claims, the invention provides a method for enhancing calibration of magneto resistive (MR) elements formed on a wafer during lapping of the MR elements. The method comprises: (1) collecting a high frequency sampling of data related to element resistance and stripe height of the MR element at a row level of the wafer during an ongoing lapping operation; (2) analyzing the data to determine accurate relationship characteristics between stripe height and resistance of the MR element; (3) providing a result of the analysis to a calibration component utilized to control lapping parameters and adjustment of lapping dimensions; and (4) dynamically controlling the lapping operation on the MR element utilizing the results with a MR sensor component (i.e., ELEs) to make adjustments to the lapping dimensions.
Operation of the invention is completed via an apparatus/system for performing in-situ calibration of stripe height and resistance characteristics of a deposited thin film resistive material. The system comprises: (1) a plurality of thin film resistive elements of the thin film resistive material having a height dimension and corresponding resistance, where the plurality of resistive elements are configured in slider rows on a quad, each separated by a kerf; (2) a plurality of elements like ELGs (ELEs) placed in alternating keys for measuring the resistance of each resistive element; (3) an electrical contact system comprising alternating ELGs and ELEs located in kerfs between elements and spaced to provide a large number of contact points; (4) a recording mechanism for periodically recording a resistance and corresponding stripe height projected from ELGs and ELEs, respectively at pre-selected lapping intervals; (5) a processor that performs statistical and mathematical analysis of the recorded data after a predetermined number of recording periods have elapsed to produce calibration parameters; (6) a control mechanism that dynamically adjusts the position of the ELEs and dynamically adjust the target and lapping pressures, which optimizes row distribution, utilizing the result of the analysis; and (7) a mechanism for effecting the lapping of the thin film resistive element utilizing the calibration parameters.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.